With the advent of dual-energy x-ray absorptiometry (DEXA) scanning for osteoporosis, a cohort of male patients has been identified with idiopathic osteoporosis. This disease has not been genetically characterized and may be a heterogeneous family of disorders. The vitamin D receptor allelle Bsm1 has been studied in several populations of persons with and without osteoporosis with conflicting results. The purpose of this study was to compare men with osteoporosis and men with high bone mineral density to see if this genotype was associated in either of these groups. Patients are healthy men 65 years of age and older with femoral neck or trochanter bone mineral density greater than or equal to 1.5 standard deviations above the age-matched mean. The men with idiopathic osteoporosis were recruited from a patient population followed at JHBP Metabolic Bone Disease Clinic. Twenty-six patients were recruited with an average age of 61.8 years, 24 Caucasian and 2 African-American men. Seventeen men had idiopathic osteoporosis (47% BB, 47% Bb, 6% bb) and 9 (33% BB, 66% Bb, 0% bb) had high bone mineral density. DNA was extracted from a 4 ml blood sample and amplified by polymerase chain reaction (PCR) for subsequent digestion with Bsm I. Genotype was determined by agarose gel analysis of Bsm I digestion products. Samples were genotyped as homozygous or heterozygosis for the Bsm I allelles (B=650 bp and b-825 bp). The unexplained absence of the bb genotype in males with high bone mineral density and relatively low ratio in males with idiopathic osteoporosis is unexplained. This could be a result of sampling bias or a true correltion of B with high bone mineral density. Further recruitment of subjects is ongoing to evaluate 100 men with either high bone mineral density or idiopathic osteoporosis.